From what I've read plants were cared for in the Pacific Northwest with changes made to support them and defined plots owned. To me it seems like they were already doing agriculture.
What else do they need to do to make the jump, and how can they?
To me it seems like the wapato could have the selective breeding that tends to make plants better for humans as in increased yields, to make it a staple crop, even if it has to be supplemented with other plants. But was it already at its maximum potential for human use? I somehow don't think that. Which suggests that even more intensive management is needed.